The plane story of galactic clusters

Why are galaxies where they are? Astronomers have turned up a hint at the way dark matter affects the large-scale structure of the universe, with observations discovering that the Milky Way and nearby galactic clusters are arranged along a plane.

The researchers, from the Australian National University, believe the arrangement of galaxies and globular clusters hints at large-scale structures based on vast filaments of dark matter.

According to lead researcher Stefan Keller of the ANU, the structures are revealed by the spatial distribution of the Milky Way’s satellite galaxies, such as the Magellanic Clouds.

Galaxies like beads on a string, say ANU astronomers.

Image: Michael Boylan-Kolchin, University of California Irvine

Rather than being randomly distributed, the paper that Keller has co-authored with Dougal Mackay and Gary Da Costa has found a planar distribution that suggests the galaxies are connected by something with sufficient gravity to maintain that structure.

Hence the suggestion that the large-scale structure is evidence of dark matter.

Keller likens the galactic structures as “beads on a string”, telling The Register that the existence of dark matter filaments would help explain why the Magellanic Clouds are located perpendicular to the plane of the Milky Way’s disk, and are feeding matter into our galaxy.

“The Magellanic Clouds, which are satellites of the Milky Way, are the source of gas that is raining down on the Milky Way and is added, slowly, to the Milky Way’s disk,” he explained.

If you model our galaxy without taking into account the possible existence of dark matter filaments, he said, the models predict a fatter disk than actually exists.

“Matter, both dark and ordinary, is drawn along these filaments to the largest local mass distribution,” he said – and in the case of his observations, that is the Milky Way, which is steadily cannibalizing the Magellanic Clouds.

Of course, the problem remains of identifying exactly what those dark matter filaments are. “We suspect that it is a weakly interacting massive particle,” he said, but noted that early results from the Large Hadron Collider “don’t look good” for these “WIMPs”. ®